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Plasmid analysis of 219 methicillin-resistant Staphylococcus aureus strains with uncommon profiles isolated in Lisbon
1Department of Microbiology, Faculty of Medicine, University of Lisbon, Portugal.
Abstract:
During the years 1986 and 1987, 219 methicillin-resistant Staphylococcus aureus (MRSA) strains were isolated in a Lisbon hospital. Antimicrobial susceptibilities and genetic analysis showed that resistance to penicillin, methicillin, erythromycin (inducible phenotype), tetracycline, gentamicin, tobramycin, kanamycin, streptomycin, neomycin and trimethoprim were chromosomally encoded. Plasmid DNA was absent from 38.8% of the isolates. Constitutive erythromycin resistance was coded by three plasmids of c. 2.3 Md, c. 2.0 Md and c. 1.6 Md. Chloramphenicol resistance was mediated by two plasmids of c. 2.9 Md and c. 1.8 Md. Small cryptic plasmids of c. 1.65 Md, c. 1.2 Md and c. 1.0 Md were also detected. The majority of the strains revealed antigen 17, were lysed by phages 75, 89 and/or 85, and were either devoid of plasmid DNA, or possessed a c. 1.6 Md plasmid coding for constitutive erythromycin resistance or a c. 1.0 Md cryptic plasmid. These observations cannot rule out that the MRSA Lisbon isolates are a homogeneous group of strains that might have a common origin, and seem to be different from MRSA recently isolated in other countries.
Insights
This study analyzed 219 methicillin-resistant Staphylococcus aureus (MRSA) strains from Lisbon, finding chromosomal encoding for most antibiotic resistance. Some MRSA strains lacked plasmids, while others carried plasmids for erythromycin or cryptic DNA.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat.
- Understanding the genetic basis of MRSA resistance is crucial for effective treatment and control.
- Previous studies have characterized MRSA isolates, but specific genetic features of Lisbon isolates require detailed investigation.
Purpose of the Study:
- To characterize the antimicrobial susceptibilities and genetic elements of MRSA strains isolated in Lisbon between 1986-1987.
- To investigate the presence and role of plasmid DNA in antibiotic resistance among these MRSA isolates.
- To determine if the Lisbon MRSA isolates represent a homogeneous group with a potential common origin.
Main Methods:
- Isolation and identification of 219 MRSA strains from a Lisbon hospital.
- Antimicrobial susceptibility testing against a panel of antibiotics.
- Plasmid DNA analysis, including detection, size determination, and characterization of resistance genes.
- Phage typing and antigen analysis for epidemiological typing.
Main Results:
- Most antibiotic resistance (penicillin, methicillin, erythromycin, tetracycline, gentamicin, etc.) was chromosomally encoded.
- 38.8% of MRSA isolates lacked plasmid DNA.
- Specific plasmids were identified, mediating constitutive erythromycin resistance (c. 2.3, 2.0, 1.6 Md) and chloramphenicol resistance (c. 2.9, 1.8 Md).
- Small cryptic plasmids (c. 1.65, 1.2, 1.0 Md) were also detected.
- Majority of strains showed antigen 17 and were lysed by specific phages, with plasmid profiles varying.
Conclusions:
- The MRSA Lisbon isolates exhibit diverse resistance mechanisms, with chromosomal encoding being predominant.
- The presence and types of plasmids varied among isolates, suggesting different genetic backgrounds or evolution.
- The findings suggest that the Lisbon MRSA isolates may form a homogeneous group with a common origin, distinct from MRSA strains found internationally.